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An Integrated Solar Power System

by paul spencer Mon Dec 3rd, 2007 at 11:38:37 AM EST

I have collected the pieces of an interesting puzzle - an experiment actually.  Y'all might be interested in the results, when they become available.  I should have some initial data within three months.

Ingredients (puzzle pieces): forty 6-volt, 180 amp-hour batteries; one 2.5 kilowatt, true-sine-wave, grid-tie inverter; 0.6 kw capability photovoltaic modules; five 4-feet by 12-feet, black rubber, solar-water-heating "pads"; two 275 gallon (U.S.) plastic water tanks; two ½ horsepower electric pumps; one water-to-air heat pump (5-ton capacity).

Diary Rescue by Migeru

Location: south-facing roof in Columbia River Gorge, 65 kilometers east of Portland, OR.  

The inverter can make switching decisions such as: 1) if no exterior power (e.g., downed transmission lines), route from batteries to house demand; 2) if house demand is less than solar-based input, charge batteries; 3) if 2) and batteries are charged, send to the exterior power grid (turn meter backwards).  OK - this is conventional stuff nowadays.

Also, water-to-air heat pumps are not only well-known, but the market is growing at an encouraging rate - encouraging because this is demonstrated to be the most efficient conventional approach to space-heating/cooling.  Basically, it uses the well-known refrigeration cycle of expansion/compression to concentrate heat in one region of the machine and to remove heat from another region.

For those who don't know about the so-called geothermal heat pump system, it is typically based on pipes set about 1.7 meters deep in the ground, where soil temperature stays fairly stable at close to 10 degrees C in the temperate zones of the world.  In Winter the refrigeration cycle is designed such that the heat pump pulls out some of the heat inherent in 10 degree water, sending, say, 5 degree water back into the pipes in the ground.  The length of the piping system is calculated to permit the water to equilibrate at the ground temperature before returning to the heat pump.  In Summer the system is valved such that the system reverses direction in terms of heat flow - the heated water goes out to the pipes in the ground.  The piping systems are typically quite long, but the extent of the trenching can be reduced by digging wider trenches and looping the pipe as it is laid.

Another less-used system (that is also becoming more common) is to use black rubber pads with small channels fabricated into the length of the pads, manifolded into pipes running width-wise at either end of the pads, to capture solar-based heat in water flowing through these channels.  In the U.S. swimming pools are sometimes warmed in the Spring and Fall by this method.  Occasionally, these pads are used in conjunction with storage tanks to provide warm/hot water for 'hydronic' heating of floors - water-carrying tubes laid in thick mortar beds under tiles, for instance.

The idea/experiment here is to combine the heating via the black pads with a water-to-air heat pump.  One ½ hp pump will drive the water from the storage tanks through the pads on the roof and back into the tanks.  A second pump will take water from the tanks to the heat pump, when a house-interior thermostat demands hot (or cold) air.

My son helped me to install the water-heating pads on my roof two weekends ago.  The last pieces were the water storage tanks, which are sitting in my driveway now.  I'm getting ready to install my tanks, pumps, and heat pump in the next few weeks.  (I want to get them up soon, so that I can start collecting temperature data vs. ambient conditions in Winter.)  After that I'll install my solar modules, grid-tie inverter, and batteries.  (Plus I will buy another 2 kw-capability of photovoltaic modules by the end of the year.)

Conditions in my neighborhood are anything but ideal. Insolation runs at about 60% of the high-prairie region just east of my county. Insolation data for this area says that I should just about cover the southern half of my roof with panels to supply about the same kwh-equivalent that I currently consume in electric resistance heating - if capture is successful.

Days here are frequently windy, and a friend - Ormond O. - predicts that the wind will actually work to pull heat out of the system - or at least to reduce the capture of the potential solar-based heat. We'll see.  If glazed systems are needed to overcome this effect, at least I won't have much invested in the rubber ones (they're quite cheap).  In addition my roof is only sloped at about 10 degrees from the horizontal; and, since we are above the 45th parallel, best angle would probably be something like 60 degrees in Winter.

Couple of interesting wrinkles to consider:
1)The tanks can be charged from rainwater on the roof;
2)Since my garden is one "floor" beneath my garage, I can water the garden with rainwater via the storage tanks;
3)In Fall, Winter, or Spring - when the rainwater is warmer than the water in the tanks, the rainwater can be used to supplant the tank water, raising the temperature and, thus, providing heat;
4)In Winter the water temperature from our city system comes in at about 10 C.  The city system is gravity-pressurized.  In the case of long-term electrical failure, the heat pump water system can be recharged from city water, and the heat pump can be run for more than one month on the batteries, assuming high-charge state initially;
5)In Summer the pump that lifts the water to the pads would be turned on at, say, midnight and off at, say, 5:00 AM.  Idea would be to radiate heat away from the pads during the coolest part of the night.  This would be for use in supporting the 'air conditioner' cycle.  (We see 35 C or above about one to two weeks per year, so air conditioning would be nice during that period.)

So - as I say - this is an experiment.  Comparing temperature changes to the various ambient conditions should provide some ability to predict viability - although viability may entail moving 80 km to the East of here.

very cool. paul, thanks for the info.

would love to see flow and wiring diagrams, pictures etc, as you install this system.

best of luck, i wish everyone could and would do what you are doing!

'The history of public debt is full of irony. It rarely follows our ideas of order and justice.' Thomas Piketty

by melo (melometa4(at)gmail.com) on Mon Nov 26th, 2007 at 03:32:49 AM EST
Great experience...!
While I understand the photovoltaic and the solar heating part, I'm not sure about what is called the "canadian well" (pipes underground using thermal mass equilibrium). This process needs quite a lot of those pipes as: Either the section is too important and it won't work, or they are small enough but you end very quickly to heat the ground around it, loosing most of it's effect...!
There is today some questioning on the biological part of having water staying still for some time in contact with air in pipes (what material? As PVC is usually banned). If the water flows regularly the linear length  of the pipes combo needed is then to big and not so interesting!

Some filters might be needed if you use that solar heated water for body use (shower, etc.) as it generates the perfect temperature for Legionella bacteria to evolve quickly !

Have you thought of a Stirling engine ? As if you have windy conditions, you can generate a mechanical movement that will get you either heat or cold... On the other side, with a solar dish focused on the head of the cylinder you can generate cold while still having a mechanical movement that could reload your batteries with a dynamo !

One point you haven't described is the change rate of air in the well insulated house ?
Most use now an air heat exchange system with the outgoing heated air loading in temperature the incoming air. The English call it the "thermal flywheel", as it is a double maze of thin steel sheets, quite easy to build or to get done. Filters are here also needed for particles, incoming as outgoing...

Some basic sketches might be interesting with the progress of your work :-)

"What can I do, What can I write, Against the fall of Night". A.E. Housman

by margouillat (hemidactylus(dot)frenatus(at)wanadoo(dot)fr) on Mon Nov 26th, 2007 at 05:50:10 AM EST
Long time no read.  Very enjoyable to find you posting again, margouillat!

Don't fight forces, use them R. Buckminster Fuller.
by rg (leopold dot lepster at google mail dot com) on Mon Nov 26th, 2007 at 10:08:30 AM EST
[ Parent ]
Ssssh... I'm trying to re-enter walking on tip toes...!

"What can I do, What can I write, Against the fall of Night". A.E. Housman
by margouillat (hemidactylus(dot)frenatus(at)wanadoo(dot)fr) on Mon Nov 26th, 2007 at 05:50:20 PM EST
[ Parent ]
in future reports.

To some of your questions:
Pipe material is typically polyurethane or PEX (cross-linked polyethylene);
Water will not be considered potable - will not be used for showers, etc.
The main drawback for the 'geothermal' approach is the length of pipe required - order of magnitude is 500 meters. Even with looping, trenching is extensive, plus the authorities require a certain displacement between the trenches - I think about two meters. So - it takes a fair amount of "yard" to accomodate. In new construction, though, the trenches could be cut under driveways or even foundations, but best not spring a leak.
As to the usefulness or effectiveness of this approach - it is proven by many installations to be one of the most energy-efficient systems for space heating in terms of energy used to run the system.

Sven notes below the 'trombe' approach. Definitely a good way to go. In fact my "pads" may need something equivalent to glazing to work well in my environment. Only possible advantages that I can see for the water-based system is the relative energy-density of water vs. air; the light weight and low cost of the "pads"; and the relative precision and ease of control of a heat pump via thermostatic switch. As I say, though, this is an experiment. Only one way to find out what works in my opinion.

As to Stirling engines - I have a sketch and some ideas on a related device. I intend to work on it concretely after retirement.

As to air exchange - I hadn't really thought much about it in the terms that you mention. Currently, there is some warm-air leakage via two bathroom vents, a fireplace chimney, and the clothes dryer vent. The heat exchanger for the heat pump is set in the middle of a finished basement. If I go to a heat-exchange mode of outside-air intake, I will have to construct some kind of pipe system. Sounds like a good idea, though.

paul spencer

by paul spencer (spencerinthegorge AT yahoo DOT com) on Mon Nov 26th, 2007 at 11:28:28 AM EST
[ Parent ]
 I completely agree,  the "canadian well" (we call it here the "Provencal well" from Provence, South of France) works. The latest "Zenith" ( covered spectacle show theatre about 10 000 public when full) in Dijon by Philippe Chaix uses that technique. I believe it's the biggest volume to use it!

But then it's only for a few hours a day (and not every days) and uses air and not water for refreshing or pre-heating the volume.

When is your retirement ? :-) That related device sounds great !

Here (in France) we have regulations for air exchanges. Meaning getting new air in at about 200 m3/h (cubic meters per hour) for a 85 square meter flat (T4- about 212 m3), so it's the full volume of the housing per hour at peak time (kitchen while preparing food and shower and toilets times).-, half of it at night...
In fact, few flats achieve that, even less house ! The electrical fans that pulls air fro toilets and kitchens are often undersized, make too much noise and break down after a few years ad are seldom replaced!!!

In cities like Paris, we believe that air is more polluted inside the flats the outside in the traffic...! Most glues used in buildings or furniture can be formaldehyde based, plus several other household products can have drastic effects on our biology, specially nowadays when there are many more young with deep allergies. So the general idea is to get air moving... Without loosing the kW's :-)

"What can I do, What can I write, Against the fall of Night". A.E. Housman

by margouillat (hemidactylus(dot)frenatus(at)wanadoo(dot)fr) on Mon Nov 26th, 2007 at 06:17:20 PM EST
[ Parent ]
A simple solution pioneered by an architect friend in Finland that I have described here before:

On a south facing roof, large flat boxes about 10 - 15 cms deep, painted black on the insides, with a glass face. The air inside the boxes heats up. The boxes are connected via plastic tubes, and on down into a cellar. A return pipe comes up from the cellar to feed already warmed air back into the boxes. The air is circulated by a single fan in the tubes, powered by a single solar cell.

The insulated cellar is filled with large granite rocks stacked to leave airspace around them. The rocks slowly heat up from the warmed air passed through them.

At night, when it is colder, the tube fan is switched to pull up warm air from the cellar, and a vent is switched to redirect the warmed air into the house, and isolate the roof tubes so warm air is only circulating from house to cellar.

You can't be me, I'm taken

by Sven Triloqvist on Mon Nov 26th, 2007 at 06:18:45 AM EST
supressed the alternative energy movement way back in 1973 so what makes you think they won't do it again!
by Lasthorseman on Mon Nov 26th, 2007 at 08:38:26 PM EST
yes they did, and it delayed us 40 years, which might prove to be the 40 years that would have made all the difference...

but the truth will out, and people put 2+2 together themselves!

solar power doesn't work, they'd say, and meanwhile it's on the space station, and half the emergency traffic lights have a pv panel perched over them!

even now here in italy, they purport to support alt. energy with 'iniziativi', but the rollout is achingly slow, because of all the glacial molasses bureaucracy, and the shadiness of some of the characters trying to 'get rich quick' on the changes not exactly inspiring trust in the enquiring citizen, brain seriously bent out of shape by having been lied to for decades, but whose ratcheting utility bills are getting his attention...

they pulled the wool but good, but you can only fool all of the people some of the time...

'The history of public debt is full of irony. It rarely follows our ideas of order and justice.' Thomas Piketty

by melo (melometa4(at)gmail.com) on Mon Dec 3rd, 2007 at 12:09:01 PM EST
[ Parent ]
Yesterday I saw an interview with Dr. Zhengrong Shih, CEO of SunTech Power Holdings, a very fast growing manufacturer of solar panels.  (Compare their stock "STP" price to traditional energy companies over the last 3 months.  Here's a chart that does it.  XLE is a traditional energy ETF with Exxon, etc.  AAPL and ISRG are in there to represent traditional hi-tech companies.)

Shih, Chinese but a citizen of Australia where he got his PhD, started his company near Singapore because they were more friendly to helping him start up - Australians just wanted to make money off him while he wants to help the world.

To isolate his company from rising raw silicon prices Shih signed very long term supply contracts.

He works out imaginative financing deals like this: a bank loans the money to buy a bunch of solar panels.  5,000 panels are installed on the roof of HP's office in San Diego.  HP pays back the bank, and the bank pays SunTech. Installation is included in the price.   Apparently the monthly cost to HP is attractive, plus being green.

SunTech currently manufactures 420 megawatts of production capacity per year.  And they don't use expensive industrial machines to assemble the panels - it is done by several thousand people, by hand.

by NHlib on Mon Dec 3rd, 2007 at 04:41:36 PM EST
[ Parent ]
I ran across this some time ago and it´s Chinese to me.  Is it worth trying to understand it?


Our knowledge has surpassed our wisdom. -Charu Saxena.

by metavision on Mon Dec 3rd, 2007 at 01:59:10 PM EST
Shading and insulating are undoubtedly useful. One question would be: what supports the bubbles' physical integrity? If the idea is to constantly replenish them, what is the energy required to do so? What is the insulation value of a collection of bubbles? Interesting idea, though.

paul spencer
by paul spencer (spencerinthegorge AT yahoo DOT com) on Tue Dec 4th, 2007 at 05:22:54 PM EST
[ Parent ]

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